The act of looking at something as you drive by. People do it when they come past an accident. Also tourists do it when they are observing the scenery when they are driving. It quite often causes traffic to slow down because the person looking generally slows down a bit to look out their window or windshield.
"That tourist in front of us is just rubber necking and causing this traffic jam."
"If that guy hadn't been rubber necking I wouldn't have been late for work."
Guy 1: "Hey I saw you hooked up with Katie last night, anything happen?"
Guy 2: "Yea, she was Muppet Necking me all night!"
Guy 1: "Aww what? Damn, you got lucky!"